Apparatus for controlling radial distribution of plasma ion density and ion energy at a workpiece surface by multi-frequency RF impedance tuning

ABSTRACT

In a physical vapor deposition plasma reactor, a multi-frequency impedance controller is coupled between RF ground and one of (a) the bias electrode, (b) the sputter target, the controller providing adjustable impedances at a first set of frequencies, said first set of frequencies including a first set of frequencies to be blocked and a first set of frequencies to be admitted. The first multi-frequency impedance controller includes a set of band pass filters connected in parallel and tuned to said first set of frequencies to be admitted, and a set of notch filters connected in series and tuned to said first set of frequencies to be blocked.

BACKGROUND

Plasma processing is employed in fabrication of integrated circuits, masks for use in photolithographic processing of integrated circuits, plasma displays and solar technology, for example. In the fabrication of integrated circuits, a semiconductor wafer is processed in a plasma chamber. The process may be a reactive ion etch (RIE) process, a plasma enhanced chemical vapor deposition (PECVD) process or a plasma enhanced physical vapor deposition (PEPVD) process, for example. Recent technological advances in integrated circuits have reduced feature sizes to less than 32 nanometers. Further reductions will require more precise control over process parameters at the wafer surface, including plasma ion energy spectrum, plasma ion energy radial distribution (uniformity), plasma ion density and plasma ion density radial distribution (uniformity). In addition, better consistency in such parameters between reactors of identical design is required. Ion density is important in PEPVD processes, for example, because ion density at the wafer surface determines deposition rate and the competing etch rate. At the target surface, target consumption (sputtering) rate is affected by ion density at the target surface and ion energy at the target surface.

Currently, uniformity of PEPVD deposition rate and deposited film properties cannot be precisely controlled, and is dependent upon chamber geometry, such as a large wafer-to-target distance. There is a need to precisely adjust or control uniformity of deposition rate, by controlling ion density distribution across the wafer surface. There is a need to precisely adjust or control uniformity of deposited film properties by controlling ion energy distribution across the wafer surface.

SUMMARY

A plasma reactor is provided for performing physical vapor deposition on a workpiece such as a semiconductor wafer. The reactor includes a chamber including a side wall and a ceiling, the side wall being coupled to an RF ground.

A workpiece support is provided within the chamber having a support surface facing the ceiling and a bias electrode underlying the support surface. A sputter target is provided at the ceiling with an RF source power supply of frequency f_(s) coupled to the sputter target. An RF bias power supply of frequency f_(b) is coupled to the bias electrode. A first multi-frequency impedance controller is coupled between RF ground and one of (a) the bias electrode, (b) the sputter target, the controller providing adjustable impedances at a first set of frequencies, the first set of frequencies including a first set of frequencies to be blocked and a first set of frequencies to be admitted. The first multi-frequency impedance controller includes a set of band pass filters connected in parallel and tuned to the first set of frequencies to be admitted, and a set of notch filters connected in series and tuned to the first set of frequencies to be blocked.

In one embodiment, the band pass filters comprise inductive and capacitive elements connected in series, while the notch filters comprise inductive and capacitive components connected in parallel. The capacitive elements of the band pass filter and of the notch filters are variable in accordance with one embodiment.

The reactor may further include a second multi-frequency impedance controller coupled between the bias electrode and RF ground and providing adjustable impedances at a second set of frequencies, the first set of frequencies comprising at least the source supply frequency f_(s). The first set of frequencies are selected from a set of frequencies that includes harmonics of f_(s), harmonics of f_(b), and intermodulation products of f_(s) and f_(b), in one embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the exemplary embodiments of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention.

FIG. 1 depicts a plasma reactor in accordance with a first embodiment.

FIG. 2 depicts the structure of multi-frequency impedance controllers in the reactor of FIG. 1.

FIG. 3 depicts a circuit implementation of a target multi-frequency impedance controller of FIG. 2.

FIG. 4 depicts a circuit implementation of a pedestal multi-frequency impedance controller of FIG. 2.

FIG. 5 depicts one embodiment if the target and pedestal multi-frequency impedance controllers.

FIG. 6 is a block diagram depicting a first method in accordance with one embodiment.

FIG. 7 depicts the different ground return paths for RF bias power controlled by a target multi-frequency impedance controller in the reactor of FIG. 1.

FIG. 8 depicts the different ground return paths for RF source power controlled by a cathode multi-frequency impedance controller in the reactor of FIG. 1.

FIG. 9 is a graph depicting different radial distributions of ion energy across a wafer or target surface that can be produced by adjusting a multi-frequency impedance controller in the reactor of FIG. 1.

FIG. 10 is a graph depicting different radial distributions of ion density across a wafer or target surface that can be produced by adjusting a multi-frequency impedance controller in the reactor of FIG. 1.

FIG. 11 is a block diagram depicting another method in accordance with one embodiment.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION

In one embodiment, a first multi-frequency impedance controller is coupled between a sputter target of a PVD reactor and RF ground. Optionally, and in addition, a second multi-frequency impedance controller is coupled between the wafer susceptor or cathode and RF ground.

The first multi-frequency impedance controller (which is connected to the ceiling or sputter target) governs the ratio of the impedances to ground through the ceiling (sputter target) and the side wall. At low frequencies, this ratio affects the radial distribution of ion energy across the wafer. At very high frequencies, this ratio affects the radial distribution of ion density across the wafer.

The second multi-frequency impedance controller (which is connected to the cathode or wafer susceptor) governs the ratio of the impedances to ground through the cathode and the side wall. At low frequencies, this ratio affects the radial distribution of ion energy across the ceiling or sputter target. At very high frequencies, this ratio affects the radial distribution of ion density across ceiling or sputter target.

Each multi-frequency impedance controller governs the impedance to ground through the ceiling (in the case of the first controller) or through the cathode (in the case of the second controller) of different frequencies present in the plasma, including harmonics of the bias power frequency, harmonics of the source power frequency, intermodulation products of the source and bias power frequencies and their harmonics, for example. The harmonics and intermodulation products may be selectively suppressed from the plasma by the multi-frequency impedance controller, in order to minimize inconsistencies in performance between reactors of the same design. It is our belief that some of these harmonics and intermodulation products are responsible for inconsistencies in reactor performance between reactors of identical design.

For very high frequencies, the first multi-frequency impedance controller's impedance to ground through the ceiling or target (with reference to the impedance through the grounded side wall) controls the radial distribution of ion density across the wafer surface is changed for fine adjustment. For low frequencies, the first multi-frequency impedance controller's impedance to ground through the ceiling or target (with reference to the impedance through the grounded side wall) controls the radial distribution of ion energy across the wafer surface is changed for fine adjustment.

For very high frequencies, the second multi-frequency impedance controller's impedance to ground through the wafer or cathode (with reference to the impedance through the grounded side wall) controls the radial distribution of ion density across the ceiling or sputter target. For low frequencies, the second multi-frequency impedance controller's impedance to ground through the wafer or cathode (with reference to the impedance through the grounded side wall) controls the radial distribution of ion energy across the sputter target or ceiling. The foregoing features provide a novel process control mechanism to regulate the reactor performance and uniformity.

In addition to governing distribution of ion energy and/or ion density across the wafer surface and across the ceiling (target) surface, the multi-frequency impedance controllers also govern the composite (total) ion density and ion energy at these surfaces through governance of impedance to ground at appropriate frequencies (e.g., low frequencies for ion energy and very high frequencies for ion density). Therefore, the controllers determine process rates at the wafer and target surfaces. Selected harmonics are tuned, depending upon the desired effect, either to promote their presence in the plasma or to suppress them. The tuning of the harmonics affects ion energies at wafer, thereby affecting process uniformity. In a PVD reactor, tuning of the ion energy affects step coverage, overhang geometry and physical film properties such as grain size, crystal orientation, film density, roughness and film composition. Each multiple frequency impedance controller can further be employed to enable or prevent deposition, etching or sputtering of the target or wafer or both, by appropriate adjustment of impedance to ground for selected frequencies, as will be described in detail in this specification. For example, in one mode, the target is sputtered while deposition is carried out on the wafer. In another mode, the wafer is etched while sputtering of the target is prevented, for example.

FIG. 1 depicts a PEPVD plasma reactor in accordance with a first embodiment. The reactor includes a vacuum chamber 100 enclosed by a cylindrical side wall 102, a ceiling 104 and a floor 106. A workpiece support pedestal 108 within the chamber 100 has a support surface 108 a for supporting a workpiece such as a semiconductor wafer 110. The support pedestal 108 may consist of an insulating (e.g., ceramic) top layer 112 and a conductive base 114 supporting the insulating top layer 112. A planar conductive grid 116 may be encapsulated within the top insulating layer 112 to serve as an electrostatic clamping (ESC) electrode. A D.C. clamping voltage source 118 is connected to the ESC electrode 116. An RF plasma bias power generator 120 of a bias frequency f_(b) may be coupled through an impedance match 122 to either the ESC electrode 116 or to the conductive base 114. The conductive base 114 may house certain utilities such as internal coolant channels (not shown), for example. If the bias impedance match 122 and bias generator 120 are connected to the ESC electrode 116 instead of the conductive base 114, then an optional capacitor 119 may be provided to isolate the impedance match 122 and RF bias generator 120 from the D.C. chucking power supply 118.

Process gas is introduced into the chamber 100 by suitable gas dispersing apparatus. For example, in the embodiment of FIG. 1, the gas dispersing apparatus consists of gas injectors 124 in the side wall 102, the gas injectors being supplied by a ring manifold 126 coupled to a gas distribution panel 128 that includes various supplies of different process gases (not shown). The gas distribution panel 128 controls the mixture of process gases supplied to the manifold 126 and the gas flow rate into the chamber 100. Gas pressure in the chamber 100 is controlled by a vacuum pump 130 coupled to the chamber 100 through a pumping port 132 in the floor 106.

A PVD sputter target 140 is supported on the interior surface of the ceiling 104. A dielectric ring 105 insulates the ceiling 104 from the grounded side wall 102. The sputter target 140 is typically a material, such as a metal, to be deposited on the surface of the wafer 110. A high voltage D.C. power source 142 may be coupled to the target 140 to promote plasma sputtering. RF plasma source power may be applied to the target 140 from an RF plasma source power generator 144 of frequency f_(s) through an impedance match 146. A capacitor 143 isolates the RF impedance match 146 from the D.C. power source 142. The target 140 functions as an electrode that capacitively couples RF source power to plasma in the chamber 100.

A first (or “target”) multi-frequency impedance controller 150 is connected between the target 140 and RF ground. Optionally, a second (or “bias”) multi-frequency impedance controller 170 is connected between the output of the bias match 122 (i.e., to either the conductive base 114 or to the grid electrode 116, depending upon which one is driven by the bias generator 120). A process controller 101 controls the two impedance controllers 150, 170. The process controller can respond to user instructions to increase or decrease the impedance to ground of a selected frequency through either of the first and second multi-frequency impedance controllers 150, 170.

Referring to FIG. 2, the first multi-frequency impedance controller 150 includes an array 152 of variable band reject (“notch”) filters and an array 154 of variable band pass (“pass”) filters. The notch filter array 152 consists of many notch filters, each notch filter blocking a narrow frequency band, one notch filter being provided for each frequency of interest. The impedance presented by each notch filter may be variable, to provide full control of impedances for each frequency of interest. The frequencies of interest include the bias frequency f_(b), the source frequency f_(s), harmonics of f_(s), harmonics of f_(b), intermodulation products of f_(s) and f_(b) and the harmonics of the intermodulation products. The pass filter array 154 consists of many pass filters, each pass filter passing (presenting a low impedance to) a narrow frequency band, one pass filter being provided for each frequency of interest. The impedance presented by each notch filter may be variable, to provide full control of impedances for each frequency of interest. The frequencies of interest include the bias frequency f_(b), the source frequency f_(s), harmonics of f_(s), harmonics of f_(b), intermodulation products of f_(s) and f_(b) and harmonics of the intermodulation products.

Referring still to FIG. 2, the second multi-frequency impedance controller 170 includes an array 172 of variable band reject (“notch”) filters and an array 174 of variable band pass (“pass”) filters. The notch filter array 172 consists of many notch filters, each notch filter blocking a narrow frequency band, one notch filter being provided for each frequency of interest. The impedance presented by each notch filter may be variable, to provide full control of impedances for each frequency of interest. The frequencies of interest include the bias frequency f_(b), the source frequency f_(s), harmonics of f_(s) and f_(b) and intermodulation products of f_(s) and f_(b). The pass filter array 174 consists of many pass filters, each pass filter passing (presenting a low impedance to) a narrow frequency band, one pass filter being provided for each frequency of interest. The impedance presented by each notch filter may be variable, to provide full control of impedances for each frequency of interest. The frequencies of interest include the bias frequency f_(b), the source frequency f_(s), harmonics of f_(s) and f_(b) and intermodulation products of f_(s) and f_(b).

FIG. 3 depicts the target multi-frequency controller with one implementation of the notch filter array 152 and the pass filter array 154. The notch filter array 152 includes a set of m (where m is an integer) individual notch filters 156-1 through 156-m connected in series. Each individual notch filter 156 consists of a variable capacitor 158 of capacitance C and an inductor 160 of inductance L, the individual notch filter having a resonant frequency f_(r)=1/[2π(LC)^(1/2)]. The reactances L and C of each notch filter 156 are different and are selected so that the resonant frequency f_(r) of a particular notch filter corresponds to one of the frequencies of interest, each notch filter 156 having a different resonant frequency. The resonant frequency of each notch filter 156 is the center of the narrow band of frequencies blocked by the notch filter 156.

The pass filter array 154 of FIG. 3 includes a set of n (where n is an integer) individual pass filters 162-1 through 162-n connected in parallel. Each individual pass filter 162 consists of a variable capacitor 164 of capacitance C and an inductor 166 of inductance L, the pass filter 162 having a resonant frequency f_(r)=1/[2π(LC)^(1/2)]. Optionally, each pass filter 162 may include, in addition, a series switch 163 to permit the pass filter to be disabled whenever desired. The reactances L and C of each pass filter 162 are different and are selected so that the resonant frequency f_(r) corresponds to one of the frequencies of interest, each pass filter 162 having a different resonant frequency. The resonant frequency of each pass filter 162 is the center of the narrow band of frequencies passed or admitted by the pass filter 162. In the implementation of FIG. 3, there are n pass filters 162 in the pass filter array 154 and m notch filters in the notch filter array 152.

The notch filter array 172 and pass filter array 174 for the second multi-frequency impedance controller 170 may be implemented in a similar manner, as depicted in FIG. 4. The notch filter array 172 includes a set of m (where m is an integer) individual notch filters 176-1 through 176-m connected in series. Each individual notch filter 176 consists of a variable capacitor 178 of capacitance C and an inductor 180 of inductance L, the individual notch filter having a resonant frequency f_(r)=1/[2π(LC)^(1/2)]. The reactances L and C of each notch filter 176 are different and are selected so that the resonant frequency f_(r) of a particular notch filter corresponds to one of the frequencies of interest, each notch filter 176 having a different resonant frequency. The resonant frequency of each notch filter 176 is the center of the narrow band of frequencies blocked by the notch filter 176.

The pass filter array 174 of FIG. 4 includes a set of n (where n is an integer) individual pass filters 182-1 through 182-n connected in parallel. Each individual pass filter 182 consists of a variable capacitor 184 of capacitance C and an inductor 186 of inductance L, the pass filter 182 having a resonant frequency f_(r)=1/[2π(LC)^(1/2)]. Optionally, each pass filter 182 may include, in addition, a series switch 183 to permit the pass filter to be disabled whenever desired. The reactances L and C of each pass filter 182 are different and are selected so that the resonant frequency f_(r) corresponds to one of the frequencies of interest, each pass filter 182 having a different resonant frequency. The resonant frequency of each pass filter 182 is the center of the narrow band of frequencies passed or admitted by the pass filter 182. In the implementation of FIG. 4, there are n pass filters 182 in the pass filter array 174 and m notch filters 176 in the notch filter array 172.

Precise control of RF ground return paths through each of the multi-frequency impedance controllers at selected frequencies is attained by the process controller 101 individually governing each of the variable capacitors 158, 164 of the first multi-frequency impedance controller 150 and each of the variable capacitors 178, 184 of the second multi-frequency impedance controller 170.

Referring now to FIG. 5, the resonant frequencies of the n pass filters 162-1 through 162-11 in the pass filter array 154 of the first (target) multi-frequency impedance controller 150 are harmonics and intermodulation products of the source and bias power frequencies f_(s) and f_(b) may include the following frequencies: 2f_(s), 3f_(b), f_(b), 2f_(b), 3f_(b), f_(s)+f_(b), 2(f_(s)+f_(b)), 3(f_(s)+f_(b)), f_(s)−f_(b), 2(f_(s)−f_(b)), 3(f_(s)−f_(b)). In this example, n=11. The resonant frequencies of the m notch filters 156-1 through 156-12 in the notch filter array 152 of the first multi-frequency impedance controller are also harmonics and intermodulation products of the source and bias power frequencies f_(s) and f_(b) may include the following frequencies: f_(s), 2f_(s), 3f_(s), f_(b), 2f_(b), 3f_(b), f_(s)+f_(b), 2(f_(s)+f_(b)), 3(f_(s)+f_(b)), f_(s)−f_(b), 2(f_(s)−f_(b)), 3(f_(s)−f_(b)). In this example, m=12. The notch filter 156-1 having the resonant frequency f_(s) blocks the fundamental frequency of the source power generator 144 to prevent it from being shorted through the impedance controller 150.

Referring still to FIG. 5, the resonant frequencies of the n pass filters 182-1 through 182-11 in the pass filter array 174 of the second (bias) multi-frequency impedance controller 170 are harmonics and intermodulation products of the source and bias power frequencies f_(s) and f_(b) may include the following frequencies: 2f_(s), 3f_(s), f_(s), 2f_(b), 3f_(b), f_(s)+f_(b), 2(f_(s)+f_(b)), 3(f_(s)+f_(b)), f_(s)−f_(b), 2(f_(s)−f_(b)), 3(f_(s)−f_(b)), in which case n=11. The resonant frequencies of the m notch filters 176-1 through 176-12 in the notch filter array 172 of the second (bias) multi-frequency impedance controller 170 are also harmonics and intermodulation products of the source and bias power frequencies f_(s) and f_(b) may include the following frequencies: f_(b), 2f_(s), 3f_(s), f_(s), 2f_(b), 3f_(b), f_(s)+f_(b), 2(f_(s)+f_(b)), 3(f_(s)+f_(b)), f_(s)−f_(b), 2(f_(s)−f_(b)), 3(f_(s)−f_(b)). In this example, m=12. The notch filter 176-1 having the resonant frequency f_(b) blocks the fundamental frequency of the bias power generator 120 to prevent it from being shorted through the impedance controller 170.

As described above, each pass filter (162, 182) may include an optional switch (163, 183, respectively) to disable the pass filter in the event that its resonant frequency is to be blocked by a notch filter. For example, each pass filter 162 of FIG. 3 can include a series switch 163, and each pass filter 182 of FIG. 4 can include a series switch 183. However, if the multi-frequency impedance controllers 150, 170 are implemented with prior knowledge of which frequencies are to be blocked and which ones are to be admitted through the respective controllers, then, within a particular controller, a notch filter would be provided for each frequency to be blocked by that controller, and no pass filter would be provided in that controller for the blocked frequencies. In such an implementation, the notch filters would be tuned only to the frequencies to be blocked while the pass filters would be tuned only to the frequencies to be admitted within an individual controller, the two sets of frequencies being mutually exclusive in one embodiment. This implementation would avoid the need for the pass filter series switches 163, 183.

FIG. 6 depicts a method of operating the reactor of FIGS. 1 through 3. In the method, the bias power current from the wafer is apportioned, as depicted in FIG. 7, between a center path to the target, I_(c), and an edge path I_(s), to the side wall. Also, source power current from the target is apportioned, as depicted in FIG. 8, between a center path to the wafer, i_(c), and an edge path i_(s), to the side wall. Thus, for RF source power at the source power frequency f_(s) from the target, the method includes establishing a center RF ground return path through the wafer via the bias impedance controller 170 and an edge RF ground return path through the side wall (block 200 of FIG. 6). For RF bias power at f_(b) from the wafer pedestal, the method includes establishing a center RF ground return path through the target via the target impedance controller 150 and an edge RF ground return path through the side wall (block 210 of FIG. 6).

In one aspect of the method, ion density over wafer center is increased while decreasing ion density over wafer edge, by decreasing impedance to ground at f_(s) through the bias multi-frequency impedance controller 170 relative to the impedance to ground at the source power frequency f_(s) through the side wall (block 215 of FIG. 6). This increases the tendency toward a center high ion density distribution depicted in solid line in FIG. 9. This step may be carried out by adjusting the resonant frequency of the pass filter 182-3 closer to the source frequency f_(s).

In another aspect, ion density is decreased over wafer center while increasing ion density over wafer edge by increasing impedance to ground at f_(s) through the bias multi-frequency impedance controller 170 relative to the impedance to ground at f_(s) through the side wall (block 220 of FIG. 6). This increases the tendency toward a center low edge high ion density distribution depicted in dashed line in FIG. 9. This step may be carried out by adjusting the resonant frequency of the pass filter 182-3 further (away) from the source frequency f_(s).

In a further aspect, ion energy over wafer center is increased while decreasing ion energy over wafer edge by decreasing impedance to ground at the bias power frequency f_(b) through the target multi-frequency impedance controller 150 relative to the impedance to ground at f_(b) through the side wall (block 225 of FIG. 6). This increases the tendency toward a center high ion energy distribution depicted in solid line in FIG. 10. This step may be carried out by adjusting the resonant frequency of the pass filter 162-3 closer to the bias frequency f_(b).

In a yet further aspect, ion energy over wafer center is decreased while increasing ion energy over wafer edge by increasing impedance to ground at f_(b) through the target multi-frequency impedance controller 150 relative to the impedance to ground at f_(b) through the side wall (block 230 of FIG. 6). This increases the tendency toward a center low edge high ion energy distribution depicted in dashed line in FIG. 10. This step may be carried out by adjusting the resonant frequency of the pass filter 162-3 further away from the bias frequency f_(b).

FIG. 11 illustrates a method for suppressing harmonics and/or intermodulation products or their harmonics at a chosen one of either the wafer surface or the target surface. Different frequencies may be suppressed at the different surfaces. This may be carried out, in one application, to optimize chamber matching among reactors of identical design, for example. In order to suppress at the wafer surface a particular frequency component corresponding to a certain harmonic or intermodulation product (block 300 of FIG. 11), plasma current components at that frequency are diverted to a surface other than the wafer surface, such as the side wall or the ceiling or target. In order to divert the undesired frequency component from the wafer to the ceiling, the impedance to ground at that particular frequency through the pedestal multi-frequency impedance controller 170 is increased (block 305 of FIG. 11). This may be accomplished by de-tuning or disabling the one pass filter in the pass filter array 174 most closely associated with that frequency (block 310), if there is one. In addition, the corresponding notch filter in the notch filter array 172 may be tuned more closely to the particular frequency (block 315). Optionally, or in addition, the undesired frequency component is drawn away from the wafer surface by diverting it to the target 140. This may be accomplished by decreasing the impedance to ground at the particular frequency through the target multi-frequency impedance controller 150, to divert the undesired components to ground through the target 140 and away from the wafer (block 320). This latter step may be accomplished by tuning one of the pass filters 156 having a corresponding resonant frequency closer to the frequency of the undesired component (block 325).

In order to suppress at the target surface a particular frequency component corresponding to a certain harmonic or intermodulation product (block 330), the impedance to ground at that particular frequency through the target multi-frequency impedance controller 150 is increased (block 335). This may be accomplished by de-tuning (or disconnecting) the one pass filter in the pass filter array 154 most closely associated with that frequency (block 340). In addition the corresponding notch filter in the notch filter array 152 may be tuned more closely to the particular frequency (block 345). Optionally, and in addition, the impedance to ground at that same frequency through the pedestal multi-frequency impedance controller 170 is decreased, to divert those components to ground away from the target (block 350). This latter step may be accomplished by tuning the one pass filter of the pass filter array 174 to the particular frequency (block 355).

Some of the foregoing steps may be employed to promote a desired frequency component at either the wafer surface or at the target surface. The plasma current frequency component may be chosen to be one which promotes or increases a particular action of the plasma, such as sputtering or deposition or etching. For example, a chosen plasma current frequency component may be directed or diverted to the target for such a purpose. This direction or diversion may be accomplished by performing the step of block 325, in which a chosen plasma current frequency component is diverted to the target 140. The diversion may be more complete by additionally performing the step of block 315 to repulse the chosen frequency component from the wafer surface.

Another chosen plasma current frequency component may be diverted to the wafer surface for a similar or other purpose (increase etch rate, deposition rate or sputter rate at the wafer surface, for example). This diversion may be accomplished by performing the step of block 355, in which a chosen plasma current frequency component is diverted to the wafer surface. This diversion may more complete by additionally performing the step of block 345 to repulse the chosen frequency component from the target surface. As one example, the chosen frequency component may be a frequency (a fundamental or harmonic or intermodulation product) that promotes a particular plasma action, such as sputtering. If it is desired to sputter the wafer without sputtering the target, then that frequency component is diverted away from the target and to the wafer by raising the impedance at that frequency through the target impedance controller 150 while reducing the impedance at the same frequency through the bias impedance controller 170. Conversely, if it is desired to sputter the target without sputtering the wafer, then that frequency component is diverted away from the wafer and to the target by decreasing the impedance at that frequency through the target impedance controller 150 while increasing the impedance at the same frequency through the bias impedance controller 170. The desired plasma effect may be obtained with a particular set of plural frequency components. In such a case, the plural frequency components are controlled in the foregoing manner using plural notch and/or pass filters operated simultaneously in accordance with the foregoing.

The foregoing features may be implemented in a plasma reactor lacking a sputter target, e.g., a plasma reactor adapted for processes other than physical vapor deposition. In such a reactor, for example, the target 140 and DC source 142 of FIG. 1 are absent, and the RF source power generator 144 and match 146 may be coupled to the ceiling 104. The ceiling 104 in such a case functions as a plasma source power applicator in the form of an electrode for capacitively coupling plasma source power into the chamber 100. In an alternative embodiment, the source power generator 144 and match 146 may be coupled to another RF source power applicator at the ceiling, such as a coil antenna for example.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. A physical vapor deposition plasma reactor, comprising: a chamber including a side wall and a ceiling, said side wall being coupled to an RF ground; a workpiece support within the chamber having a support surface facing the ceiling and a bias electrode underlying the support surface; a sputter target at said ceiling; an RF source power supply of frequency f_(s) coupled to said sputter target, and an RF bias power supply of frequency f_(b) coupled to said bias electrode; a first multi-frequency impedance controller coupled between RF ground and one of (a) the bias electrode, (b) the sputter target, and providing respective impedances at a first set of frequencies, said first set of frequencies comprising harmonics of f_(s), harmonics of f_(b), and intermodulation products of f_(s) and f_(b), said first multi-frequency impedance controller comprising: a set of respective first filters connected in series or in parallel, each one of said respective first filters having a respective band centered at a respective frequency, and each respective first filter being individually tuned whereby the respective frequency coincides with a respective one of said first set of frequencies.
 2. The apparatus of claim 1 wherein: said first filters are connected in series and comprise respective notch filters, and each said respective frequency is a respective block frequency; said first impedance controller further comprises: a set of respective pass filters connected in parallel, each one of said respective pass filters having a respective pass band centered at a respective pass frequency and each respective pass filter being individually tuned whereby the respective pass frequency corresponds with a respective one of said first set of frequencies; and said apparatus further comprising a controller coupled to said pass filters and said notch filters.
 3. The apparatus of claim 2 wherein: each respective one of said pass filters comprises inductive and capacitive elements connected in series and defining a respective resonant frequency corresponding to the respective pass frequency, the pass frequency of each pass filter being different from that of the other pass filters; and each respective one of said notch filters comprises inductive and capacitive components connected in parallel and defining a respective resonant frequency corresponding to the respective block frequency, the block frequency of each notch filter being different from that of the other notch filters.
 4. The apparatus of claim 3 wherein the capacitive elements of said pass filters and of said notch filters have capacitances that are variable, said apparatus further comprising a process controller governing the variable capacitance of each of said capacitive elements independently from the variable capacitances of the other capacitive elements.
 5. The apparatus of claim 1 wherein said first multi-frequency impedance controller is coupled between RF ground and the sputter target.
 6. The apparatus of claim 5 further comprising: a second multi-frequency impedance controller coupled between said bias electrode and RF ground and providing adjustable impedances at a second set of frequencies.
 7. The apparatus of claim 6 wherein said second set of frequencies comprise harmonics of f_(s), harmonics of f_(b), and intermodulation products of f_(s) and f_(b).
 8. The apparatus of claim 6, further comprising a process controller coupled to said first and second multi-frequency impedance controllers, said process controller controlling impedances at said first set of frequencies in said first multi-frequency impedance controller and impedances at said second set of frequencies in said second multi-frequency impedance controller.
 9. The apparatus of claim 8 wherein: said first and second multi-frequency impedance controllers each comprise an array of notch filters connected in series and an array of band pass filters connected in parallel and individually tuned to respective resonant frequencies; each of said filters comprises a variable reactance element; said process controller governs said variable reactance elements.
 10. The apparatus of claim 1 further comprising a D.C. power supply coupled to said sputter target.
 11. A plasma reactor, comprising: a chamber including a side wall and a ceiling, said side wall being coupled to an RF ground; a workpiece support within the chamber having a support surface facing the ceiling and a bias electrode underlying the support surface; a source power applicator at said ceiling; an RF source power supply of frequency f_(s) coupled to said source power applicator, and an RF bias power supply of frequency f_(b) coupled to said bias electrode; a first multi-frequency impedance controller coupled between RF ground and one of (a) the bias electrode, (b) the source power applicator, and providing selected impedances at a first set of frequencies, said first set of frequencies comprising harmonics of f_(s), harmonics of f_(b), and intermodulation products of f_(s) and f_(b), said first multi-frequency impedance controller comprising: a set of respective first filters connected in series or in parallel, each one of said respective first filters having a respective band centered at a respective frequency, and each respective first filter being individually tuned whereby the respective frequency coincides with a respective one of said first set of frequencies.
 12. The apparatus of claim 11 wherein: said first filters are connected in series and comprise respective notch filters, and each said respective frequency is a respective block frequency; said first impedance controller further comprises: a set of respective pass filters connected in parallel, each one of said respective pass filters having a respective pass band centered at a respective pass frequency, and each respective pass filter being individually tuned whereby the respective pass frequency corresponds with a respective one of said first set of frequencies; and said apparatus further comprising a controller coupled to said pass filters and said notch filters.
 13. The apparatus of claim 12 wherein: each respective one of said pass filters comprises inductive and capacitive elements connected in series and defining a respective resonant frequency corresponding to the respective pass frequency, the pass frequency of each pass filter being different from that of the other pass filters; and each respective one of said notch filters comprises inductive and capacitive components connected in parallel and defining a respective resonant frequency corresponding to the respective block frequency, the block frequency of each notch filter being different from that of the other notch filters.
 14. The apparatus of claim 13 wherein the capacitive elements of said pass filters and of said notch filters have capacitances that are variable, said apparatus further comprising a process controller governing the variable capacitance of each of said capacitive elements independently from the variable capacitances of the other capacitive elements.
 15. The apparatus of claim 11 wherein said first multi-frequency impedance controller is coupled between RF ground and said source power applicator.
 16. The apparatus of claim 15 further comprising: a second multi-frequency impedance controller coupled between said bias electrode and RF ground and providing adjustable impedances at a second set of frequencies.
 17. The apparatus of claim 16 where said second set of frequencies comprise harmonics of f_(s), harmonics of f_(b), and intermodulation products of f_(s) and f_(b).
 18. The apparatus of claim 16, further comprising a process controller coupled to said first and second multi-frequency impedance controllers, said process controller controlling impedances at said first set of frequencies in said first multi-frequency impedance controller and impedances at said second set of frequencies in said second multi-frequency impedance controller.
 19. The apparatus of claim 1 further comprising a source RF impedance match connected between said RF source power supply and said sputter target, and a bias RF impedance match connected between said RF bias power supply and said bias electrode.
 20. The apparatus of claim 11 further comprising a source RF impedance match connected between said RF source power supply and said source power applicator, and a bias RF impedance match connected between said RF bias power supply and said bias electrode. 